For laminated iron core manufacturing, a method of punching a plurality of thin steel sheets (thin plates), which are magnetic steel sheets, while the plurality of thin plates are placed in a stacked state to obtain a laminated iron core is conventionally suggested for the purpose of productivity enhancement.
When, for example, punching two thin plates in a stacked state, the two stacked thin plates are fixed to each other so as not to move, and then sent into a molding device (punching device).
More concretely, the following methods are known: a method to join the thin plates by caulking or spot welding at positions separated by a specified distance from each other in a feeding direction of the stacked thin plates (for example, refer to Patent Literature 1); and a method to integrate the thin plates by welding end faces in one side of the thin plates (for example, refer to Patent Literature 2). Commonly, joining by caulking is widely adopted in view of productivity enhancement and cost reduction of facilities and others.
In a usual case where punching thin plates with a molding device, to precisely place thin plates 70 at a working position in a molding device 71, as shown in FIGS. 3A and 3B, pilot holes 72 are formed through the thin plates 70, pilot pins 73 of the molding device 71 are then inserted into the pilot holes 72 to position the thin plates 70, and hereby a punching process is performed. After the punching process finishes, the pilot pins 73 are pulled from the pilot holes 72 by being raised as an upper die 74 is raised, and then the thin plates 70 are sent to a next punching station. Note that, in FIGS. 3A and 3B, a reference character: 75 represents a lower die where a die is fixed, and a reference character: m represents a center line.